Grease composition



United States Pat ent 3,505,224 GREASE COMPOSITION Paul R. McCarthy, Allison Park, and Thomas R. Orem,

Blawnox, Pa., assignors to Gulf Research & Development Company, Pittsburgh, Pa., a corporation of Pennsylvania No Drawing. Filed Oct. 26, 1967, Ser. No. 678,197 Int. Cl. C10m 7/48, 7/30, 7/02 U.S. Cl. 252-28 9 Claims ABSTRACT OF THE DISCLOSURE A grease composition for lubricating bearings operating at temperatures up to about 600 F. and speeds up to about 20,000 revolutions per minute comprises:

(a) 80 to 95 percent by weight of a liquid polyorgano siloxane, e.g., silicone oil;

(b) 2 to 10 percent by weight of a 1,3,5-triazine compound melting above about 600 F., e.g., ammel-ine;

(c) 2 to 10 percent by weight of a finely-divided silica,

e.-g., Cab-O-Sil; and

(d) 0.5 to 4 percent by weight of an alkaline earth metal hydroxide, e.g., calcium hydroxide.

The weight ratio of (b) or (c) is between about 1:5 and 5:1.

This invention relates to an improved lubricating composition and more particularly to a lubricant having the consistency of a grease suitable for high temperature lubrication.

The trend in design of modern aircraft has accentuated the need for a lubricant having the consistency of a grease which will lubricate anti-friction bearings operating at high rotational speeds and high temperatures. Considerable progress has been made in recent years in producing improved thickened lubricants for aircraft. For example, lubricating compositions having the consistency of a grease are now available for lubricating bearings operating at 10,000 to 20,000 revolutions per minute at temperatures up to about 400 F. However, great difficulty has been encountered in producing a lubricating composition having the consistency of a grease which will effectively lubricate bearings operating at speeds up to about 20,000 revolutions per minute and at temperatures up to about 600 F. for prolonged periods of time.

In order to produce a lubricating composition having the consistency of a grease which will effectively lubricate bearings operating at temperatures up to 600 F. it is necessary to employ as the lubricating oil base a material which is highly resistant to thermal degradation at ternperatures up to 600 F. In addition, the lubricating oil base must have the ability to lubricate and remain fluid both at high and ambient temperatures over a prolonged period of time without excessive volatilization, gumming or coking. While some mineral oils especially hydrotreated mineral oils are sufiiciently stable to provide adequate lubrication when used under moderately elevated temperatures, the volatility of mineral oils is such that they do not give adequate lubrication at temperatures in the order of 600 F. Synthetic oils are substantially more resistant to thermal degradation than mineral oils. Synthetic oils, parioularly the polyorgano siloxanes known as the silicone oils in addition to being more resistant to thermal degradation than mineral oils also have high viscosity indices making their use at high and ambient temperatures especially desirable. Thus, the lubricating oil base employed in the composition of the present invention is a synthetic lubricating oil.

Lubricating compositions having the consistency of a grease which employ a synthetic lubricating oil as the base 3,505,224 Patented Apr. 7, 1970 oil can be prepared by adding a thickening agent such as a metal soap of a fatty acid or certain triazine compounds alone and in combination with other thickening agents including organophilic siliceous materials, or-gano hydantoins, bis-pyrazolones, tetraphenylphthalyl compounds and the like. In preparing lubricants thickened with such agents, the amount of thickening agent used, whether a single agent or a mixture of thickening agents, has been rather high, being in the order of about 30 percent or more by weight of the total grease composition. The use of such a high amount of thickening agent is undesirable from an economic standpoint where the agent is expensive. The use of a large amount of thickening agent is further undesirable in that the use of a large amount of some agents frequently imparts undesirable properties to the lubricant.

According to current production techniques, many bearings are prepacked with lubricating compositions and then stored for long periods before they are used. Thus, an effective lubricant for prepacked bearings must have a consistency to assure adequate retention in the bearings during storage. However, the lubricant must not be too hard to give adequae lubrication on subsequent use. A soft grease tends to flow at normal atmospheric temperature and consequently such a grease may drain from the bearing prior to being placed in service, thus giving rise to inadequate lubrication when the bearing is used. A hard grease does not flow from the bearing during storage, but a hard grease does not have adequate flow properties to supply necessary lubrication during use of the bearing. A satisfactory lubricating grease composition for use at 600 F. must therefore have a consistency which will give adequate lubrication at temperatures of 600 F. without flowing from the bearing during storage at normal atmospheric temperature. A satisfactory lubricant for use in bearings operating at speeds up to 20,000 revolutions per minute and at temperatures up to about 600 F. should have a dropping point above about 650 R, an unworked penetration (ASTM D217) of about 210 to about 350 and a worked penetration (60 strokes) of about 225 to about 360, the difference between the worked and the unworked penetration being less than 50 units. The lubricant should have a performance life of at least hours when determined by a procedure outlined by the Coordinating Research Council, Research Technique for the Determination of Performance Characteristics of Lubricating Grease Antifriction Bearings at Elevated Temperatures, CRC Designation L-35.

We have discovered that a lubricating composition which will pass the above requirements and has other satisfactory lubricating characteristics for an extended period of time when used to lubricate bearings operating at temperatures up to about 600 F. and speeds up to about 20,000 revolutions per minute can be obtained by incorporating into a synthetic lubricating oil between about 5 and about 20 percent by weight based on the weight of the lubricating composition of a mixture of a 1,3,5-triazine compound melting above about 600 F., finely-divided silica and an alkaline earth metal hydroxide. The weight ratio of triazine compound of finely-divided silica is within the range of 1:5 to 5:1 and the alkaline earth metal hydroxide comprises about 0.5 to about 4 percent by weight of the total composition. Thus, the improved lubricating composition of our invention comprises a dispersion in a synthetic lubricating oil of about 5 to about 20 percent by weight of a mixture of a 1,3,5- triazine compound melting above about 600 F., finelydivided silica and an alkaline earth metal hydroxide, wherein the weight ratio of the triazine compound to the silica is within the range of about 1:5 to about 5:1.

The amount of the combined 1,3,5-triazine compound, finely-divided silica and alkaline earth metal hydroxide which we use may vary depending upon the particular lubricating base employed and upon the characteristics desired in the ultimate composition. In any event, however, the total amount of the 1,3,5-triazine compound, finely-divided silica and alkaline earth metal hydroxide does not exceed 20 percent by weight of the total composition and is preferably within the range of about to about 15 percent by weight of the total composition. The Weight ratio of the triazine compound to the finely-divided silica will vary within rather narrow limits depending upon the characteristics desired in the ultimate composition. In general, the weight ratio of the 1,3,5-triazine compound to the finely-divided silica is about 1 :5 to about 5:1. When ratios above about 5:1 are employed, the grease composition has a tendency to soften during storage and frequently leaks from bearings prepacked with such a grease composition. An especially preferred composition comprises a liquid polyorgano siloxane lubricating oil thickened to the consistency of a grease with about 7 to about 13 percent by weight of a mixture of ammeline and finely-divided silica in a weight ratio of about 1:3 to about 3:1 and about 0.5 to about 4 percent by weight of calcium hydroxide.

The 1,3,5triaziue compounds which are employed according to the invention are limited to those compounds melting above about 600 F. Exemplary of such com pounds are 2,4-diamino-1,3,5-triazine; 2,4-diamino-6-hy droxy-l,3,5-triazine (ammeline); 2,4-dihydroxy-6-amino- 1,3,5-triazine (ammelide); and 2,4-dihydroxy-6-pyridyl-1, 3,5-triazine. While compounds melting below 600 F. can he used to produce grease compositions for use at temperatures below 600 F., such compounds are not satisfactory thickening agents for grease compositions used to lubricate bearings operating at high rotational speeds at temperatures in the order of 600 F. and higher for prolonged periods of time.

The 1,3,5-triazine compounds can be prepared according to known chemical procedures. Neither the compounds per se nor their preparation constitutes any portion of the invention. For example, 2,4-dihydroxy-6-pyridyl-1,3,5-triazine can be prepared by stirring for thirty minutes at room temperature a mixture of cyanuric chloride (18.5 gm., 0.1 mole), pyridine (100 ml.) and water (500 ml.). The reaction mass is then filtered and the filtrate is concentrated on a water bath to give a product comprising 2,4dihydroXy-6-pyridyl-l,3,5-triazine having a melting point above about 752 F.

The amount of the 1,3,5-triazine compound used may vary depending upon the particular oil with which the triazine compound is to be blended and upon the properties desired in the final lubricating composition. In general, the triazine compound comprises about 2 to about 10 percent by weight of the total composition. The amount of the triazine compound and the finely-divided silica are inversely related in that as the amount of one is increased in the composition the amount of the other is decreased. Thus, as the upper limit of the triazine is approached, the lower limit of the finely-divided silica is approached. The weight ratio of triazine to finely-divided silica is between about 1:5 and about 5:1.

The finely-divided silica which is employed in the lubricating composition of this invention is not to be confused with silica gels, silica aerogels, or other precipitated silicas. The silica which we employ is a finely-divided amorphous silica. The most common process for manufacturing a finely-divided silica useful in the composition of our invention is by the high-temperature vapor-phase hydrolysis of silicon tetrachloride. However, a suitable finely-divided silica can also be made by the high-temperature, vapor-phase thermal decomposition of silicon compounds such as silicon esters and also the high-temperature, vapor-phase hydrolysis of silicon compounds with superheated steam, e.g., the steam hydrolysis of silicon esters or silanes. The amount of the finely-divided amorphous silica employed in the Composition of the invention 4 is a small amount in the order of about 2 to about 10 percent by weight of the total composition. As disclosed hereinabove, the amount of the finely-divided silica and the triazine compound are inversely related in that as the amount of one is increased the amount of the other is proached; and, as the 2 percent limit of finely-divided silica is approached, the 2 percent limit of triazine is approached; and, as the 2 percent limit of finely-divided silica is approached, the 10 percent limit of triazine is approached. The weight ratio of finely-divided silica to triazine is between about 1:5 and about 5:1, preferred ratios being within the range of 1:3 to 3: 1.

The alkaline earth metal hydroxide which is employed according to the invention can be either chemically pure or commercial grades thereof. The hydroxides of the metals calcium, barium, strontium and magnesium can be powdered or finely divided such as colloidal calcium hydroxide, barium hydroxide, strontium hydroxide and magnesium hydroxide. Of these compounds, calcium hydroxide is especially preferred in preparing lubricating compositions of the invention. The amount of the alkaline earth metal compound which we use may vary depending upon the particular lubricating base employed and upon the characteristics desired in the ultimate composition. The alkaline earth metal hydroxide comprises about 4 to about 45 percent by weight of the total weight of the triazine compound and the finely-divided silica. :In general, the alkaline earth metal hydroxide comprises about 0.5 to about 4 percent by weight of the total grease composition.

The synthetic lubricating oil which is employed in the composition of the invention is a liquid polyorgano siloxane having a high phenyl content and diphenylmethylsilyl end groups. The polyorgano siloxanes can be obtained by hydrolyzing and polymerizing a mixture of diphenylmethylchlorosilane, dimethyldichlorosilane and diphenyldichlorosilane preferably in a ratio of 1:1:1, respectively, according to procedures known to those familar with the art. While the polyorgano siloxanes are generally a mixture of polymers, 2. general formula representing the polymer mixture by an ideal molecule is as follows:

where x and y can be from 1 to 10 or more. An ideal molecule of a polyorgano siloxane having diphenylmethylsilyl end groups and a molecular weight of 954 is represented by the formula 3 s 5) z io 3 z l 2 s s z z e s 2 a The polyorgano siloxane content of the compositions prepared according to this invention comprises about to about percent by weight to the total composition.

The lubricating composition of this invention can contain conventional lubricant additives, if desired, to improve other specific properties of the lubricant without departing from the scope of the invention. Thus, the lubricating composition can contain a filler, a corrosion and rust inhibitor, an extreme pressure agent, an anti-oxidant, a metal deactivator, a dye and the like. Whether or not such additives are employed and the amounts thereof depend to a large extent upon the severity of the conditions to which the composition is subjected and upon the stability of the synthetic lubricating oil base in the first instance. Since the polyorgano siloxanes, for example, are in general more stable than mineral oils, they require the addition of very little, if any, oxidation inhibitor. When such conventional additives are used they are generally added in amounts between about 0.01 and about 5 percent by weight based on the weight of the total composition.

In compounding a composition of the present invention, various mixing and blending procedures may be used. According to one embodiment of the invention, the

synthetic lubricating oil, the 1,3,5-triazine compound, the finely-divided silica and the alkaline earth metal hydroxide together with conventional lubricant additives, if desired, are mixed together at room temperature for a period of about to 30 minutes to form a slurry. During this initial mixing period some thickening is evidenced. Some lumps may be formed. The slurry thus formed is then subjected to a conventional milling operation in a ball mill, a colloid mill, homogenizer or similar device used in compounding greases to give the desired degree of dispersion.

Lubricating compositions within the scope of the invention comprising a dispersion in a major amount of a liquid polyorgano siloxane of a small amount, suflicient to thicken the polyorgano siloxane to a grease consistency, of a mixture of a 1,3,5-triazine compound melting above about 600 F., finely-divided silica and an alkaline earth metal hydroxide, wherein the weight ratio of the 1,3,5 triazine compound to the finely-divided silica is about 1:5 to about 5:1 and the alkaline earth metal hydroxide comprises about 0.5 to about 4 percent by weight of the total composition are illustrated in Table I.

to less than 1 percent. Cab-O-Sil is an extremely fine silica with particles ranging in size from 0.015 to 0.020 micron.

In preparing the illustrative lubricating compositions of Table I, the oil, the triazine, the calcium hydroxide and the silica are mixed at room temperature for a period of 10 to minutes. The slurry thus formed is passed twice through a Premier Colloid Mill set at a stator-rotor clearance of 0.0015 inch.

In order to illustrate the lubricating characteristics of grease compositions of the invention when used to lubricate bearings operating at 600 F. and at rotational speeds of 20,000 revolutions per minute. Pope spindles were used in a test procedure similar to that outlined by the Coordinating Research Council Tentative Draft (July, 1954), Research Technique for the Determination of Performance Characteristics of Lubricating Grease in Antifriction Bearings at Elevated Temperatures, CRC Designation L-35. According to the CRC L- test method, the test bearings are packed with 3.5 cc. (or equivalent weight) of grease. Because of the extremely short life of bearings packed with 3.5 cc. of grease, the present evaluations were TAB LE I A B C D E F G H I Composition percent by weight:

Lubricating oil:

QF-6-7039 1,3,5-triazine compound:

2,4diamino-1,3,5-triazine 2,4-diaminc-G-hydroxy-l,3,5-triazin 2,4dihydroxy-6-amino-1,3,5-trlazine 2,4-dihydroxy-6-pyridyl-l,3,5-triazine Magnesium hydroxide Alkaline earth metal hydroxide content, percent a g 1 8.3 6. Ratio oiTriazinezCab-O-Srl 1:2 1:

1 Ammeline. E Ammelide. 3 Based on triaziue compound plus CabO-Su.

The synthetic lubricating oils in the lubricating compositions shown in Table I are synthetic oils known as QF-67024 Fluid and QF-6-7039 Fluid each of which is marketed by Dow-Corning Corporation. QF-6-7024 Fluid is considered to be a methylphenylsiloxane polymer wherein the end silicon atoms are substituted to a high degree by two phenyl groups and one methyl group. The material is highly resistant to radiation. QF67024 Fluid has as typical characteristics a viscosity at 100 F. of about 930 to 1030 SUS, a viscosity at 210 F. of about 90 to 100 SUS, a viscosity index of about 108 to 110 and a pour point of +10 to +20 F. It is believed that the types of side chains present and their approximate molar percentages (in brackets) in QF-6-7024 are phenyl (65), methyl attached through silicon to methyl (25) and methyl attached through silicon to phenyl (10). An ideal molecule of a polyorgano siloxane having this analysis is as follows:

The oil known as QF67039 Fluid is also considered to be a methylphenylsiloxane polymer inhibited against deterioration and otherwise similar to QF-6-7024 Fluid.

The Cab-O-Sil employed in the compositions shown in Table I is a finely-divided amorphous silica marketed by Godfrey L. Cabot, Inc. This silica is a submicroscopic particulate silica prepared in a hot gaseous environment (1100 C.) by the vapor-phase hydrolysis of a silicon compound. On a moisture-free basis, this silica is 99.0 to 99.7 percent silicon dioxide which is practically free from contaminating metallic salts. Gravimetric analyses fail to detect the presence of any calcium or magnesium. The iron content has been found to be about 0.004 percent and volatile matter removed on ignition at 1000 C. amounts made by packing the bearings completely full with about 6 to 8 grams of grease and using either a standard end cap with no additional grease or a special end cap holding a reservoir of about 10 grams of additional grease. The bearing assembly containing an eight-ball SAE No. 204 ball bearing is mounted on a horizontal spindle and is subjected to a radial load of 5 pounds. The portion of the spindle upon which the test bearing assembly is located is encased in a thermostatically controlled oven. By this means the temperature of the bearing can be maintained at a desired elevated temperature which in the tests reported hereinafter was 600 F. The spindle is driven by a constant belt-tension motor drive assembly, capable of giving spindle speeds of 20,000 revolutions per minute. The spindle is operated on a cycling schedule consisting of a series of periods, each period consisting of 20 hours running time and 4 hours shutdown time. The test continues until the lubricant fails. The lubricant is considered to have failed when any one of the following conditions occurs, (1) spindle input power increases to a value approximately 300 percent above the steady state condition at the test temperature; (2) an increase in temperature at the test bearing of 20 F. over the test temperature during any portion of a cycle; or (3) the test bearing looks or the drive belt slips at the start or during the test cycle. In the performance life test reported in Table II, the life in hours is an average of at least two separate tests run on the same composition.

In preparing the illustrative lubricating compositions of Table II, the oil, the ammeline, the calcium hydroxide and the Cab-O-Sil are mixed at room temperature for a period of 10 to 30 minutes. The slurry thus formed is passed twice through a Premier Colloid Mill set at a stator-rotor clearance of 0.002 inch. The approximate make-up and properties of the thickened lubricating compositions thus prepared are set forth in Table II.

8 tions W, X and Y which contain 35 and 36 percent by Weight of thickener.

TABLE II J K L M N O P Q R S T U V Composition, percent by weight:

Synthetic lubricating oil (QF-fi-7039) 92 87. 51 86. 88. 00 88. 00 88. 00 88. 00 88. 50 88. 00 88. 0 86. 50 85. 50 90. 00 Ammeline 3 3. 7 5. 57 3. 67 2. 75 7. 33 8. 25 4. 71 4t 71 4. 5 4. 71 4. 71 3. 86 Cab-O-Sil 4 4. 99 7. 43 7. 33 8. 25 3. 67 2. 75 6. 20 6. 29 6. 0 6. 29 6. 29 5. 14 Calcium hydroxide 1 3. 75 1. 00 1. 00 1. 00 1.00 1. 00 0. 50 1. 00 1. 5 2. 50 3. 50 1.00 Calcium hydroxide content, perc 14. 3 42. 9 7. 7 0. 1 9. 1 9. 1 9. 1 4. 5 9.1 14. 3 22. 7 31.8 11. 1 Ratio of Ammeline: Cab-O-Sil 1:1. 33 1:1. 33 1:1. 33 1:2 1:3 2:1 3:1 1:1. 33 1:1.33 1:1. 33 1:1.33 1:1.33 1:1. 33 Ins ection:

Dropping point, F. (ASTM D56642) 650+ 650+ 650+ 650+ 650+ 650+ 650+ 650+ 650+ 650+ 650+ 650+ 650+ Penetration (D-1403):

Unworked (Conv. to D-217) 321 287 246 223 212 321 347 246 242 269 253 240 279 Worked (Conv. to D-217) l 347 324 261 249 227 339 355 265 283 298 265 265 324 Worked minus unworked 26 37 15 26 15 18 8 19 41 29 12 16 45 Average performance life, hrs. at 600 F.

1 Based on Ammeline plus Cab-O-Sil.

The long performance life of compositions of the in- While our invention has been described with reference vention at a high rotational speed and a high temperature 20 to various specific examples and embodiments, it will be is self-evident from the data in Table II. It will be noted understood that the invention is not limited to such exthat average performance lives of 110 to 233 hours were amples and embodiments and may be variously practiced obtained when compositions of the invention were tested within the scope of the claims hereinafter made. in bearings operating at 600 F. and at rotational speeds We claim: of 20,000 revolutions per minute. It will be noted further 1. A lubricating grease composition comprising a disthat all of the above compositions have dropping points persion in a major amount of a liquid polyorgano siabove 650 F., unworked penetrations within the range loxane of about 5 to about 20 percent by weight of a of 210 and 350, worked penetrations (60 strokes) within mixture of a 1,3,5-triazine compound melting above the range of 22 5 to 360 and differences between unworked range of about 1:5 to about 5:1 and the alkaline earth and worked penetrations less than 50 units. metal hydroxide, wherein the weight ratio of the 1,3,5-

In order to illustrate the advantageous characteristics of triazine compound to finely-divided silica is within the compositions of the invention when compared with other range of about 1:5 to about 5:1 and the alakaline earth compositions containing either no ammeline or large metal hydroxide comprises about 0.5 to about 4 percent amounts of ammeline and ammeline to Cab-O-Sil ratios by weight of the total composition. outside the scope of the present invention, comparative 2. A lubricating grease composition comprising a distests were made the results of which are summarized in persion in a major amount of a liquid polyorgano silox- Table III. ane of about 2 to about 10 percent by weight of a 1,3,5-

TABLE III W 1 X 1 Y 1 V 2 J2 Composition, percent By Weight:

Lubricating Oil QF67039 65 64 92 mmeline I 35 34 34 3. 86 3 Cab-O-Si] 1 5. 14 4 Calcium hydroxide e 1 1. 00 1 Calcium hydroxide content, percent 2. 0 11. 1 14. 3 Ratio of Ammeline:Cab-O-Sil 34:1 1:1.33 121.33 Inspection:

Dropping Point, F 650+ 650+ 650+ 650+ 650+ Penetration D-1403:

Unworked (Conv. to D-217) 362 302 321 279 321 Worked, 60 strokes (Conv. to D217) 351 399 328 324 347 Average Performance Life, Hours at 600 20,000 r.p.rn 156 154 90 144 233 scope of the invention.

2 Compositions .T and V are compositions within the scope of the invention.

3 Based on Ammeline plus Cab-O-Sil.

It will be noted from the data in Table III that compositions of the invention (Compositions J and V) which contain only 8 and 10 percent by weight of a mixture of ammeline, Cab-O-Sil and calcium hydroxide are at least as hard or harder than Compositions W, X and Y which contain from 35 to 36 percent by weight of total thickener. While the average performance lives of Compositions W and X are above hours, the consistency of these greases is such that the greases tend to leak from prepacked bearings. The consistency of Composition Y is satisfactory for prepacking bearings, but the performance life is low. Even though Compositions W, X and Y have some of the desired characteristics of a grease for prepacking bearings which are intended for high temperature service, they do not possess all of the desirable characteristics exhibited by Compositions J and V of Table III and Compositions I to V of Table II. The improved characteristics of Compositions J to V over Compositions W, X and Y is indeed surprising when it is considered that Compositions J to V contain only 8 to 14.5 percent by weight of thickening agents as compared with Compositriazine compound melting above about 600 F., about 2 to about 10 percent by weight of finely-divided silica and about 0.5 to about 4 percent by weight of an alkaline earth metal hydroxide wherein the weight ratio of the 1,3,5-triazine compound to finely-divided silica is within the range of about 1:5 to about 5:1.

3. The lubricating composition of claim 2 wherein the 1,3,5-triazine compound is 2,4-diamino-l,3,5-triazine.

4. The lubricating composition of claim 2 wherein the 1,3,5-triazine compound is ammeline.

5. The lubricating composition of claim 2 wherein the 1,3,5-triazine compound is ammelide.

6. The lubricating composition of claim 2 wherein the 1,3,5-triazine compound is 2,4-dihydroxy-6-pyridyl- 1,3,5-triazine.

7. A lubricating grease composition comprising a dispersion in a major amount of a liquid polyorgano siloxane of about 2 to about 10 percent by weight of ammeline, about 2 to about 10 percent by weight of finelydivided silica and about 0.5 to about 4 percent by weight of calcium hydroxide wherein the weight ratio of ammeline to finely-divided silica is about 1:3 to about 3:1.

8. A lubricating grease composition comprising a dispersion in a major amount of a liquid polyorgano siloxane of a mixture of about 7 to about 13 percent by weight of ammeline and finely-divided silica wherein the weight 5 ane of about 3 percent by weight of ammeline, about 4 10 percent by weight of finely-divided silica and about 1 percent by weight of calcium hydroxide.

References Cited UNITED STATES PATENTS 3,117,085 1/1964 Rees et al. 25228 3,160,590 12/1964 McCarthy 252-28 DANIEL E. WYMAN, Primary Examiner I. VAUGHN, Assistant Examiner US. Cl. X.R.

@3 3 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,505,224 Dated p i 7. 1970 Inventor) Paul R. McCarthy and Thomas Ro Orem It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, line 25 "or" should read to Column 4, line 6 "proached; and, as the 2" should read decreased. Thus, as the 10 Column 6, line 13 the period should be a comma Column 7, last line of Table II, "20,000 p.m" should read 20, 000 r.p.m.

, under Column Q in Table II, the last figure "5" should read 155 Column 8, line 29 "range of about 1:5 to about 5:1 and the" should read about 600 F. finely-divided silica and an line 32 "alakaline" should read alkaline SIGNED AM; 5mm

(SEAL) mm E- 33. Edward M. Emir. Gmmlaaioner 0t Patents Atteating Officor 

